Composition for treating surfaces of flat objects to produce predetermined separation points to plurality of such flat objects arranged at least partially in a pile

ABSTRACT

A composition containing an anti-static agent and a lubricant for treatment of a surface of a flat article ( 2 ) so as to define point of separation of a plurality of at least partly superimposed flat articles. Due to the lubricant, the friction coefficient between the treated surface and a surface of an adjacent article and, therefore, the static friction between the two articles is reduced. Due to the anti-static agent, static charging of the treated article and, therefore, adhesion between articles obtainable through static charging is reduced. In a plurality of superimposed, flat articles statically charged in a d.c. voltage field, the named two effects produce a displacement at the location of a treated surface, when a displacement force ( 11 ) with a component parallel to the principal surfaces of the articles is applied to the plurality of articles.

BACKGROUND OF THE INVENTION

The present invention relates to a composition used for the treatment ofsurfaces of flat articles. A surface of a flat article treated with thecomposition forms a predetermined separation point in a plurality of atleast partly superimposed flat articles, i.e. a predetermined pointwhere the plurality of superimposed flat articles can be selectivelyseparated. The flat articles are, for example, made from paper,cardboard, fabric, felt or plastic. The plurality of flat articles to beseparated may be a multi-page printed product of paper, plastic orcardboard, which is to be opened at a given point, or may be a stack orscale formation of printed products or flat articles of cardboard,fabric, felt or plastic from which a specific number of articles to beremoved by separation at a predetermined point.

Superimposed, flat articles are frequently separated from one another byshoving a separating element such as a separating wedge between thearticles to be separated. The more congruent, thin and sensitive tomechanical damage the articles in question are, the more difficult it isto successfully effect a separation using a separating element. On theone hand, it is difficult to aim the element precisely at apredetermined point and, on the other hand, the risk of the separatingelement damaging the narrow sides or edges of the flat articles is notnegligible.

Therefore, superimposed, flat articles are advantageously displacedagainst one another parallel to their principal surfaces, prior to aneffective separation. By such displacement, areas of the principalsurfaces of individual articles are exposed, which areas are much bettersuited for being acted on by a mechanical separating element than thenarrow side areas of the articles.

CH-440339 describes a method for displacing relative to each other twodirectly superimposed articles within a plurality of superimposedarticles wherein a displacement force having a component parallel to theprincipal surfaces of the articles is employed. In this method, there isno action on individual narrow sides or edges of the articles. To enablethe mentioned displacement to take place between two specific articlesof the plurality of superimposed articles (predetermined separationpoint), while the other articles remain substantially undisplaced withrespect to one another, the adhesion between the two specific articlesis reduced compared with the adhesion between the other articles bymeasures suitable for reducing the friction coefficient between the twospecific articles.

Measures for reducing the friction coefficient include treating at leastone of the surfaces to be displaced relative to each other with alubricant or smoothing it or positioning a sliding film between thearticles to be displaced. Examples of lubricants are waxes,high-viscosity silicone oils or dry lubricants.

Building upon the teaching of the aforementioned patent, CH-534588describes how a stack of flexible sheets is made separable at aplurality of different, predetermined points, by applying frictioncoefficient reducing measures to different, predetermined sheets innon-overlapping areas. The stack is separated at a specific one of thepredetermined separation points by directing the displacement force tothe corresponding treated area.

It has been found that the processes and the lubricants used in themethods according to CH-440339 and CH-534588 give satisfactory resultsin many applications. However, it has been found also that in othercases the reliability with which the displacement is effected exactly inthe predetermined point is not adequate, so that the method cannot beused when high demands are made. Such cases include the separation ofpages of multi-page printed products for the purpose of opening theproduct at a predetermined point. This is especially so when theindividual pages of the printed products are made from a very smooth orcorrespondingly coated material and therefore adhere very little to oneanother, and/or when the individual pages of the printed products aremade from different materials with different friction characteristics.

SUMMARY OF THE INVENTION

In a patent application of the same applicant and filed in parallel withthe present application, a method for the separation of a plurality ofat least partly superimposed, flat articles at a predetermined point isdescribed. Using this method it becomes possible to solve separatingproblems in application areas in which the known methods cannot beapplied, and/or to attain better results than are possible with theknown methods.

An object of the present invention is to provide a composition for thetreatment of surfaces of flat articles. The composition is to be used inthe aforementioned method according to the parallel application, inorder to produce the predetermined separation point.

The method described in the parallel application is based on the factthat the adhesion between superimposed, flat articles can be increasedby static charging of their surfaces. According to the method of theparallel application, a static charge is produced on the surfaces of thesuperimposed, flat articles, by passing the articles through an electricd.c. voltage field oriented substantially perpendicular to the principalsurfaces of the articles. Due to the effect of the field, dipoles areoriented or charges are displaced perpendicular to the principalsurfaces and positive or negative charges are concentrated on the twosurfaces of each of the articles. These charges cause electricattraction forces between the surfaces of superimposed articles and,therefore, increase the mutual adhesion.

The effect of the static charging of surfaces of superimposed, flatarticles is reduced or prevented for at least one of two surfacesparticipating at a predetermined separation point, by treating thesurface beforehand with an anti-static agent. Due to the limitedconductivity of the anti-static agent, charges cannot concentrate on thetreated surface or they are very rapidly compensated. Thus, passagethrough the voltage field causes no adhesion increase at the separationpoint or at least much less adhesion increase than it causes betweennon-treated surfaces. Therefore, the treated surfaces can be movedrelative to each other by a lower force than is necessary for displacingnon-treated surfaces, which displacement by low force distinguishes theseparation point.

Application of a static charge for increasing the adhesion between flatarticles not to be separated combined with a planned application ofanti-static agent for suppressing the effect at a separation point canalso be combined with the reduction of the friction between the flatarticles to be separated by applying a lubricant, as describedhereinbefore as prior art. Since for such a combination the anti-staticagent and the lubricant are advantageously used on the same surfaceareas, the two agents can be applied and used simultaneously in the formof a mixture in a single method step. It is also possible to add aluminophore to the anti-static agent or to the mixture of anti-staticagent and lubricant, the luminophore being useful for checking theseparation at the predetermined separation point with the aid ofluminescence sensors.

The composition according to the invention is a mixture comprising ananti-static agent and a lubricant. The mixture may comprise additionalcomponents such as a luminophore.

BRIEF DESCRIPTION OF THE DRAWINGS

These and further features of the present invention will be apparentwith reference to the following description and drawings wherein FIG. 1diagrammatically illustrates successive method steps using an example ofa stack comprising five superimposed, flat articles.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The method in which the composition according to the invention is to beused is described in greater detail in connection with FIG. 1, whichillustrates successive method steps using the example of a stack 1comprising five superimposed, flat articles 2. The stack is to beseparated by displacing the two upper articles with respect to the threelower articles. Thus, the predetermined separation point is locatedbetween the upper surface of the third article and the lower surface ofthe fourth article within stack 1.

Before or during stacking articles 2, at least one of the surfacesparticipating at the separation point is treated, e.g. coated with ananti-static agent 3 or preferably with the inventive compositioncontaining an anti-static agent and a lubricant.

The surface treated with the inventive composition 3 constitutes withinthe stack one of the surfaces to be displaced relative to each other. Itis obviously also possible and even advantageous in certainapplications, to treat not only one surface of the separation point, butinstead treat both surfaces participating at the separation point withthe composition.

The stack 1 is then exposed to a d.c. voltage field, wherein the fieldlines are oriented substantially perpendicular to the principal surfacesof the articles. For this purpose the stack is passed between twoelectrodes 10, e.g. between two plates or rods to each of which adifferent constant potential is applied. By the effect of the field,dipoles are oriented or charges are displaced within the flat articles.Between the two surfaces of an article a potential difference is builtup or the surfaces of the article are statically charged(diagrammatically represented by small plus and minus signs in FIG. 1).These charges are opposed at superimposed surfaces of adjacent articlesand cause electric forces of attraction between the articles.

At surface points where the composition according to the invention acts,little or no charge can build up as a result of the increased surfaceconductivity, so that in such surface areas the forces of attractionbetween the articles are correspondingly lower.

Immediately after static charging, a displacement force (arrow 11), e.g.acting on the stack surface and having a component parallel to theprincipal surfaces of the articles is applied to the stack 1. By thisdisplacement force 11 the two surfaces in the stack adhering least toone another and showing the least friction between each other aredisplaced relative to one another, even if the force does not act at theseparation point but acts, for example, on the stack surface.

By displacing two articles of the stack against one another, areas 12 ofprincipal surfaces of these articles are exposed and can be acted onwith mechanical means in order to effectively separate the articles ofthe stack. For such an action the risk of damaging the articles is muchlower than for an action on narrow sides (edges) of articles as isnecessary for a separation without prior displacement. In addition, theexposed principal surfaces define the separation point in such a waythat it cannot be missed by a mechanical separating element.

The anti-static agent contained in the composition according to theinvention is, for example, an anti-static agent known from the plasticsindustry. The anti-static agent comprises conductive particles (e.g.carbon black, carbon fibers, nickel-coated mica, steel fibers oraluminum platelets or the conductive pigment Minatec® sold by Merck inDarmstadt) distributed in ultra-fine manner in a matrix, or ioniccompounds (e.g. quaternary ammonium salts), surfactants (e.g. glycolesters, glycol ethers or esters and salts of fatty acids) or hygroscopicsubstances (e.g. glycerol or polyglycol), which are used as such or inthe form of aqueous or alcoholic solutions.

The lubricant contained in the composition according to the invention isa lubricant usable in the aforementioned methods according to CH-440339and CH-534588. It is, for example, a wax, which can be a natural wax(e.g. beeswax), a chemically modified, originally natural wax (e.g.hydrogenated jojoba wax, paraffin wax produced from petroleum) or asynthetic wax (e.g. polyethylene glycol wax), a high-viscosity siliconeoil or a suitable plastic (e.g. Teflon).

For the preparation of the composition according to the invention thecomponents are merely mixed together and part of the components canoptionally be brought into a liquid or at least a plastic state. Thefinished composition is liquid or pasty or solid in lump form or in theform of granules or powder.

The treatment of the surfaces involves spraying or application with aroller for liquid or pulverulent compositions or for compositions in themelted state. Subsequent treatment of the treated surfaces with heat,for example, may be necessary in order to fix the composition to thesurface. Solid compositions are advantageously applied by direct rubbingonto the surface to be treated or by rubbing off with the aid of abrush.

Preferred embodiments of the composition according to the inventioncomprise a wax or a plastic (lubricating component), in which theconductive particles (conductive component) are incorporated. Suchcompositions can be very easily rubbed onto paper surfaces.

A specific embodiment of the inventive composition consists of paraffinwax and the aforementioned pigment Minatec®. This composition isparticularly suitable for the treatment of printed products, because itis invisible when applied to paper and scarcely otherwise detectable bythe reader. The weight fraction of the wax is preferably in the rangebetween 55 and 75%, more preferably between 66 and 67%.

To enable the composition according to the invention to be applied byspraying, the composition can additionally contain a solvent or water.

Further embodiments of the composition according to the invention areobtained by mixing any of the aforementioned anti-static agents with anysuitable lubricant. For specific applications, advantageous compositions(both as regards components and as regards concentrations of theindividual components) are to be established experimentally.

What is claimed is:
 1. Composition for the treatment of surfaces of flatarticles (2) for producing predetermined separation points in aplurality of said articles being at least partially superimposed,wherein the composition comprises a mixture of an anti-static agent forreducing static charging of a treated surface in a d.c. voltage fieldand a lubricant for reducing a friction coefficient between the treatedsurface and another surface.
 2. Composition according to claim 1,further comprising a solvent or water.
 3. Composition according to claim1, further comprising a luminophore.
 4. Composition according to claim1, wherein the anti-static agent consists at least partly ofelectrically conductive particles, of an ionic compound, of a surfactantor of a hygroscopic substance.
 5. Composition according to claim 1,wherein the lubricant comprises a wax, a high-viscosity silicone oil ora plastic.
 6. Composition according to claim 1, wherein the compositionis liquid or pulverulent and can be applied by spraying or rollerapplication to the treated surface.
 7. Composition according to claim 1,wherein the composition is in granular form and is brought into a liquidor plastic state for application.
 8. Composition for the treatment ofsurfaces of flat articles (2) for producing predetermined separationpoints in a plurality of said articles being at least partiallysuperimposed, wherein the composition comprises an anti-static agent forreducing static charging of a treated surface in a d.c. voltage fieldand a lubricant for reducing a friction coefficient between the treatedsurface and another surface, and wherein the anti-static agent is aconductive pigment and the lubricant is paraffin wax.
 9. Compositionaccording to claim 8, wherein the paraffin wax represents 55 to 75% ofthe weight of the composition.
 10. Composition according to claim 8,wherein the paraffin wax represents 66 to 67% of the weight of thecomposition.
 11. Composition according to claim 1, wherein thecomposition is solid and is applied by rubbing onto the treated surface.